/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/Drawing/TriangleSetComponent.h
Add a triangle with the given vertices, normal, Color, and Material
ID of the triangle created
int32 AddTriangle ( const FVector & A, const FVector & B, const FVector & C, const FVector & Normal, const [FColor](API\Runtime\Core\Math\FColor) & Color, [UMaterialInterface](API\Runtime\Engine\Materials\UMaterialInterface) * Material )